On Fri, 21 Mar 2025, Kienan Stewart via lttng-dev <lttng-dev@lists.lttng.org> wrote: > Hi Lakshya, > > On 3/21/25 8:52 AM, Gour DEV wrote: >> Thanks Kienan for digging this and explaining the behaviour, [...] >> Also, I thought using --buffers-global >> <https://lttng.org/man/1/lttng-enable-channel/v2.8/#doc-opt--buffers-global> >> would >> be better for me as I could know how much memory will be required but looks >> like that option is only available for kernel tracking, it would be very >> good if this option could be available for user buffering also, but that >> could come later. >> > > Global buffers for UST is planned for the next release. The trade-off of > using it is that tracing overhead will increase (as the buffers are no > longer per-CPU), but in exchange for a potentially lower memory > footprint particularly in situations where not all possible CPUs are online. >
Little correction here. `--buffers-global' is the ownership of the buffers (UID vs PID vs system). The next release introduces the buffers allocation policies `per-{cpu,channel}'. Therefore `--buffers-global' will still be only available for the kernel domain, AFAIK. User-space however will be able to allocate a single ring-buffer for a given channel (actually it depends on the buffer ownership UID vs PID), thus reducing the amount of memory used, for that channel, by a factor proportional to the number of CPUs possible on the system. [...] Thanks, Olivier -- Olivier Dion EfficiOS Inc. https://www.efficios.com